Question

A state Motor Vehicle Department requires learners to pass a written test on the motor vehicle laws of the state. The exam consists of twenty true-or-false questions, of which eighteen must be answered correctly to qualify for a permit. In how many different ways can a learner who answers all the questions on the exam qualify for a permit

Answer 1

211 ways

Explanation:

Given :

Number of questions = 20

Number of correct correct questions to be answered in other to qualify should be atleast 18

Hence,

Correct questions could be either 18, 19 or 20 ;

Using combination :

nCr = n! ÷ (n-r)!r!

20C18 = 20! / (20 - 18)!18!

20C18 = (20* 19) / (2 * 1) = 190 ways

20C19 = 20! / (20-19)!19!

20C19 = 20 / 1 = 20 ways

20C20 = 20! / 0! 20! = 1 ways

Hence, total number of possible ways = (190 + 20 + 1) = 211 ways